Crop an image displayed in a Canvas

Question

I have a canvas tag:

I want to add a crop functionality, so I

Answer 1

Create a new canvas at destination size, draw in the cropped image using drawImage() and insert that canvas into the DOM avoiding using img and data-uri:

var ccanvas = document.createElement("canvas"),
    cctx = ccanvas.getContext("2d");

ccanvas.width = w;
ccanvas.height = h;

// draw with crop arguments
cctx.drawImage(image_src,  x, y, w, h,  0, 0, w, h);
//                         ^^^^^^^^^^ source region
//                                      ^^^^^^^^^^ dest. region

// insert cropped image somewhere in the DOM tree:
document.body.appendChild(ccanvas);

window.onload = function() {

  var img = document.getElementById("image_src");

  document.body.appendChild(region2canvas(img, 150, 60, 220, 200));
}

function region2canvas(img, x, y, w, h) {
  var ccanvas = document.createElement("canvas"),
    cctx = ccanvas.getContext("2d");

  ccanvas.width = w;
  ccanvas.height = h;

  // draw with crop arguments
  cctx.drawImage(img, x, y, w, h, 0, 0, w, h);

  return ccanvas;
}

<img src="http://i.imgur.com/kWI4Cmz.png" id="image_src">

Answer 2

The key to cropping from one image is that the context's drawImage method allows us to render a cropped section of the source image to the canvas.

context.drawImage(img, sx, sy, sw, sh, dx, dy, dw, dh);

img - Source image object
sx - Source x
sy - Source y
sw - Source width
sh - Source height
dx - Destination x
dy - Destination y
dw - Destination width
dh - Destination height

Answer 3

Create a new canvas, and copy the selected portion to that new canvas, and then get the toDataURL() from that new canvas.

Answer 4

Use the method getImageData with the selected rectangle coordinates. For example:

let imageData = ctx.getImageData(65, 60, 100, 100);

Then create a secondary canvas with the desired sizes and use putImageData to set the pixels:

let canvas1 = document.createElement("canvas");
canvas1.width = 100;
canvas1.height = 100;
let ctx1 = canvas1.getContext("2d");
ctx1.rect(0, 0, 100, 100);
ctx1.fillStyle = 'white';
ctx1.fill();
ctx1.putImageData(imageData, 0, 0);

Finally use toDataURL to update the image:

dstImg.src = canvas1.toDataURL("image/png");

See the full sample I've prepared for you in CodePen